1. Technical Field
The present invention generally relates to field emission devices, and more particularly to a field emission device based on carbon nanotube array. The present invention also relates to a method for manufacturing field emission devices.
2. Discussion of Related Art
Carbon nanotubes produced by arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). Carbon nanotubes can transmit an extremely high electrical current and emit electrons easily at a very low voltage of less than 100 volts, which makes them a very promising potential material for field emission applications.
A conventional carbon nanotubes field emission device includes a cathode substrate and a carbon nanotubes layer formed thereon and functioning as an emitter. Field emission devices are widely used for field emission displays (FEDs), vacuum electron source and in other fields.
One conventional method for manufacturing carbon nanotubes field emission device is a screen-printing method. The screen-printing method mainly includes the steps of mixing carbon nanotubes into a paste material and then printing the paste material onto a cathode substrate. However, the surfaces of carbon nanotubes tend to be covered in the paste material and are therefore unable to combine with the cathode substrate directly, as a result it is difficult to control emittion state of carbon nanotubes using a cathode substrate. Furthermore, orientation of tips of carbon nanotubes when used as emitters is inconsistent, so it is difficult to control uniformity and stability of a carbon nanotubes field emission device.
The other conventional method for manufacturing a carbon nanotube field emission device includes the steps of: forming a metal catalyst layer on a substrate; etching the metal catalyst layer to form isolated nano-sized catalytic metal particles; growing carbon nanotubes from said isolated nano-sized catalytic metal particles using a thermal chemical vapor deposition (CVD) process; and purifying the carbon nanotubes in-situ. The carbon nanotubes formed by the above-described method are vertically aligned on the substrate. However, the above-described method is performed at a temperature in the range from 700° C. to 1000° C., thus the materials that can be used in the cathode substrate are restricted to those materials which can withstand high temperatures. Furthermore, tips of carbon nanotubes array are not formed in one plane, and the field emission can be uneven as a result. Moreover, the efficiency for utilizing carbon nanotubes is poor due to the fact that only one carbon nanotube element can be produced at a time.
What is needed, therefore, is a field emission device and a method for manufacturing the same, that can overcome the above problems.